The present invention relates to inhibition of marine growth on or marine biofouling of surfaces in marine environments, and more particularly to the use of specific substances as a agent for prevention of marine biofouling of solid surfaces, and to a method of inhibiting marine biofouling of solid surfaces.
With time, solid surfaces in marine environments will be covered with several different species of plants and animals. Such marine growth or biofouling is a considerable problem in the shipping business and other marine industries, such as aquatic cultures and marine oil and gas prospecting. Untreated ship hulls or other untreated underwater surfaces are rapidly fouled by growth thereon of marine plants and animals, and such growth highly increases friction, which in the case of ships among other things results in increased fuel consumption. To owners of leisure craft in Sweden and many other countries, the acorn barnacle is one of the most unwanted marine biofouling organisms. When fully grown, the acorn barnacle is responsible for a considerable amount of the biofouling-induced water resistance, and in addition, the acorn barnacle is difficult to remove by mechanical means from the surface on which it has attached itself.
One way of preventing marine biofouling of surfaces is to use paint comprising various types of toxic substances, such as tributyl tin oxide (TBT) or copper. The use of paints of this kind is, however, highly harmful to the environment and/or to individuals. For example, it has been found that oyster cultivations may be affected, and that the contents of such paints or toxicants are high in marine sedimentation. The use of these toxic substances thus is prohibited in many countries and more countries are expected to follow suit.
Among xe2x80x9cnon-toxicxe2x80x9d methods are particularly noted high-pressure flushing of ship hulls or mechanical removal of the organisms. Most of these methods are, however, time-consuming and therefore expensive.
On the Swedish west coast, like on the North-Atlantic coasts generally, the settlement of the acorn barnacle (Balanus) is a problem of particular magnitude. The fully-grown acorn barnacle is an attaching crustacean that surrounds itself with hard calcareous plates and forms a volcano the size of about one centimeter and of high mechanical strength. The acorn barnacle has different stages of free-swimming larvae, the last stage of which is called cyprid. With the aid of protruding appendages (cirri), the larva scans solid surfaces for suitable locations on which to establish itself. In connection with the establishment a xe2x80x9cgluexe2x80x9d known as balanus cement is secreted from special glands on the appendages, by means of which the larva attach itself to the surface. After establishment, the animal undergoes a transformation or metamorphosis and becomes an adult individual.
The present invention relates to the removal of marine growth or biofouling in an ecologically acceptable manner.
One object of the invention is the use of an aromatic compound substituted with at least one heterocyclic amine and possibly also additional substituents, or a functionally analogous derivative thereof as an agent for the prevention of marine biofouling of a solid surface.
Another object of the invention is a method for the inhibition of marine biofouling of a solid surface, according to which method at least one aromatic compound which is substituted with at least one heterocyclic amine and possibly with additional substituents, or a functionally analogous derivative thereof, is applied on said surface.
The present invention has many advantages. For example, the substances in accordance with the invention are comparatively harmless compared with the toxic substances presently used in ship hull paints, such as tributyl tin oxide. Indeed, several of the substances in accordance with the invention are so harmless that they are approved as pharmaceutical preparations for internal use.
As already mentioned, the present invention relates to the use of an aromatic compound substituted with at least one heterocyclic amine and possibly also additional substituents, or a functionally analogous derivative thereof, as an agent for the prevention of marine growth, known as biofouling, on a solid surface.
By the expression xe2x80x9caromatic compoundxe2x80x9d as used herein should be understood an organic compound comprising at least one flat ring having three conjugated double bonds. One example of an aromatic compound of this kind is benzene.
By the expression xe2x80x9cheterocyclic aminexe2x80x9d as used herein is to be understood a heterocyclic compound comprising an amino group (xe2x80x94NH2) or a substituted amino group.
By the expression xe2x80x9cfunctionally analogous derivativexe2x80x9d of the compounds according to the invention as used herein is to be understood all structural and biological analogues of the compounds in accordance with the invention that have essentially the same settling-inhibiting effect on biofouling as the compounds in accordance with the invention.
The aromatic substituted compounds used in accordance with the invention are particularly suitable to prevent biofouling of the kind formed by settling crustacean organisms, particularly acorn barnacles and most particularly acorn barnacles of the genus Balanus, and by settling polychaetes, particularly the tube building polychaetes Hydroides elegans. 
Acorn barnacles are hermaphrodites with internal fertilization. The pelagian larvae are called nauplius and feed on microorganisms of various kinds until they have stored sufficient nourishment to metamorphose into the last larval form, called cyprid larva. The cyprid larva is highly specialised to find a suitable solid surface. It has a highly developed sensorial system and proceeds by trial and error, xe2x80x9cwalkingxe2x80x9d across the surface with the aid of tentacles or cirri. The cirri also contain glands discharging a sticky protein secretion acting as a xe2x80x9cgluexe2x80x9d. When the cyprid has found a suitable surface the glue production is taken over by two larger paired glands. The cyprid then metamorphoses into an adult individual. During this period the individual also grows from approximately 0.1 mm to one or a few centimeters. The establishment of the cyprid on the solid surface is known as settling.
The aromatic substituted compounds used in accordance with the invention preferably are imidazoles or imidazolines. The compounds most preferably used are medetomidine, (xc2x1)-4-[1-(2,3-dimethylphenyl)-ethyl]-1H-imidazole-mono-hydrogen chloride of formula I below, or clonidine, 2-(2,6-di-chloro-anilino)-2-imidazoline of formula II below. 
It is also possible to use a combination of several aromatic substituted compounds in accordance with the invention or derivatives thereof.
An explanation that in no way restricts the invention of the reason why these compounds are efficient in inhibiting biofouling could be that they disturb or block the transmission of signals to the effector cells needed in order for e.g. cyprid larvae, acorn barnacles and hydrozoans to establish themselves or settle.
The aromatic substituted compounds used in accordance with the invention preferably are enclosed in a polymer, and preferably a polymer allowing slow or delayed release of the aromatic substituted compounds. One example of a suitable polymer is an acrylic polymer. The polymer is then applied on the surface in question, and in water the compounds in accordance with the invention will be released slowly from the polymer. The attachment of marine biofouling substances to the surface thus will be disturbed in a manner preventing settlement.
The aromatic substituted compounds in accordance with the invention are intended to inhibit biofouling in marine environments.
The aromatic substituted compounds in accordance with the invention are for example highly suitable for prevention of biofouling of ship hulls. For this application it may be suitable to incorporate the compound in paint intended for application on ship hulls. It is also possible to incorporate the compound in cleaning solutions intended for washing ship hulls or to rinse the ship hull with a solution of the aromatic substituted compound in accordance with the invention in order to thus achieve a biofouling-inhibiting effect. It appears as if the compounds in accordance with the invention somehow bind to the surface and in this manner produce a long-lasting effect. The aromatic substituted compounds could also be used in combination with treatments of a mechanical nature, such as high-pressure flushing, in order to increase the effect further.
The aromatic substituted compounds in accordance with the invention are highly suitable for prevention of biofouling of piping through which flows seawater. In this case it is possible to pass the aromatic substituted compound through the pipes in pulses and in this manner produce a remaining biofouling-inhibiting effect. The treatment may be repeated when needed.
The invention will be illustrated further by means of the following examples which are in no way intended to restrict the scope of protection of the invention.